Constructing dual charge transfer tunnels within highly charge-confined COFs for efficient photosynthesis of hydrogen peroxide from water and air

Abstract Insufficient charge separation and sluggish two-electron water oxidation reaction are two critical factors restricting the photosynthesis performance of hydrogen peroxide (H2O2) from naturally abundant water and air by metal-free covalent organic frameworks (COFs). Herein, we develop a facile strategy to simultaneously boost charge separation efficiency and water oxidation capability through constructing short and rapid charge transfer tunnels within highly charge-confined COFs via replacing phenyl with pyrimidine. Compared to single charge transfer tunnel within lowly charge-confined COF-APM with pyrimidine, dual charge transfer tunnels are constructed within highly charge-confined COF-BPM with bipyrimidine due to the ground-state charge transfer between para-carbon and meta-nitrogen, which significantly accelerates the intermolecular charge transfer process and prevents charge recombination. This strategy also decreases the energy barrier of rate-determining water oxidation in H2O2 photosynthesis and thus promotes the effective generation of the key *OH intermediates, facilitating the generation of H2O2 with the production rate of 5521 μmol g−1 h−1 from water, oxygen, and light without sacrificial reagents or additional energy consumption by COF-BPM. Furthermore, COF-BPM can also efficiently produce H2O2 under broad pH condition, in widely available real water, on floatable foam sheet, in continuous-flow reactor, and in scaled-up reactor using natural solar light for water decontamination.